Forage and grain yields of dual-purpose triticale as influenced by the integrated use of Azotobacter chroococcum and mineral nitrogen fertilizer

Abstract

The utilization of dual-purpose cereals is encouraged in the Mediterranean environments to fill a feed gap during the winter season. Triticale is a promising dual-purpose crop for forage and grain production. Studies on the variations in productivity and quality of dual-purpose triticale under variable fertilization management are scarce. This study was carried out during winter 2018/2019 and 2019/2020, in Northern Egypt, to evaluate the performance of triticale grown in dual-purpose and grain-only production systems under variable mineral N (mN) rates (zero, 25, 50, 75% of the recommended), accompanied with Azotobacter chroococcum (AC) seed inoculation, as well as 100% mN application without AC. The application of 50% mN with AC seed inoculation resulted in an average of 7.23, 7.27 t ha-1, forage and grain yields, respectively. Moreover, forage and grain crude protein reached 125.57, and 200.60 g kg-1, respectively. Forage fiber fractions were nonsignificantly variable among the fertilizer treatments. Azotobacter chroococcum seed inoculation, thus, allowed for the reduction of the used amount of mN to 50% without sacrificing the forage and grain yields and protein content. In the dual-purpose system, an average of 7.23 t ha-1 forage yield was obtained with little reduction in the grain yield (19% reduction in average). Meanwhile, grain CP content was higher in dual-purpose system (201.38 g kg-1) than in grain-only system (182.98 g kg-1). In similar conditions to the current study, it is recommended to expand the production of dual-purpose triticale in the winter while reducing mN fertilizer rate to 50% in combination with AC seed inoculation. Introduction Ac ce pt ed p ap er Sustainable agriculture encourages the integration of crop and livestock production systems, in order to make the maximum benefit out of the available agricultural inputs, especially in the developing countries suffering from increased populations and limited resources. However, one of the main challenges facing this mixed farming system is the exposure of livestock to seasonal feed gaps, especially in the winter. Thus, there is a pressing need to expand the utilization of dualpurpose winter cereals, as a successful strategy to fill the feed gap in the winter season (Bell et al. 2015). These are crops that are cut during the vegetative growth stage, early in the winter, and then left till maturity and grain production. This practice is highly encouraged, especially in the Mediterranean countries to narrow the gap between feed demand and supply (Sadreddine 2016; Rajae et al. 2017; Salama 2019). Triticale (X Triticosecale Wittmack) is a hybrid crop species developed by crossing two cereal crops; i.e., wheat (Triticum spp.) and rye (Secale cereale L.). It combines the best of both crops, the nutritional value of wheat along with the hardiness and nutrient-use efficiency of rye (Ayalew et al. 2018). Thus, triticale became an alternative cereal crop, mainly grown for grain production, in environments suffering from nutrient deficiency, biotic and abiotic stresses (Blum 2014; Liu et al. 2017). In 2018, triticale covered a global area of around 4 million hectares, with a total grain production of 13.5 million tons (FAOSTAT 2018). Interest has been developed in utilization of triticale as forage since the 1970s (Baron et al. 2015). When densely grown as forage, its large canopy permits high light interception and its abundant root system allows for better soil attachment and nutrient absorption (Ayalew et al. 2018). In addition, its good performance, even in less favorable environments, gives it a special advantage over other cool-season forages (Blum 2014). Being a drought tolerant crop, it proved distinction particularly in semi-arid and arid environments of the developing countries (Bilgili et al. 2009). It was, thus, proposed as a Ac ce pt ed p ap er replacement dual-purpose crop in regions where environmental conditions limit the productivity of rye, wheat, barley and oat (Baron et al. 2015; Giunta et al. 2015). The success of a dual-purpose production system is greatly dependent on the applied agricultural practices, amongst is the fertilization management. Nitrogen (N) fertilization is a key agricultural input, especially in poor, low-fertility soils. In a dual-purpose system, N availability plays a crucial role in determining the crop’s regrowth ability after cutting (Hajighasemi et al. 2016). However, the continuous application of mineral N fertilizer, that is frequently lost in several forms, leads to its deficiency in the soil (Bilal et al. 2017), in addition to being a major cause of environmental pollution (Salama and Badry, 2020). Moreover, the increasing prices of the mineral fertilizers is adding an additional financial burden on the farming systems especially in the developing countries (Salama 2019). Thus, the need to find more affordable, yet environmentally-friendly alternatives, is continuously increasing. Hence, the integration of biofertilizers, known for their nitrogen fixing potentials, with mineral N is a highly recommended practice to decrease the use of mineral fertilizers and, thus, limit their harmful environmental effects. Azotobacter species are a group of free-living, non-symbiotics nitrogen fixing microbes, that reported a significant contribution to the yield improvement of cereals (Aazadi et al. 2014). The inoculation of oat with Azotobacter reduced the amount of mineral N from 120 kg ha-1 to 80 kg ha-1 (Bilal et al. 2017). In addition, Azotobacter, known as plant growth promoting rhizobacteria (PGPR), proved significant impact on plant growth and development through, occupying the rhizosphere and secreting growth promoting metabolites, increasing nutrient use efficiency and, ultimately boosting biological N fixation (Jnawali et al. 2015). Among the various Azotobacter species, Azotobacter chroococcum is known for its significant impact on crop production and soil fertility (Wani et al., 2016). It is, however, evident that the application of only bio-fertilizers does Ac ce pt ed p ap er not give the maximum boost to crop productivity, and, thus, partial substitution of mineral fertilizer with bio-fertilizer is suggested to achieve the best results from the cropping system (Habiba et al. 2018). Studies evaluating the application of PGPB as seed inoculants have been mostly focused on genotypes exclusively recommended for grain production, with few researches on dual-purpose crops (Quatrin et al., 2019). In this regard, research results reported variations in the yield and quality of dual-purpose wheat, oat and sorghum (Quatrin et al., 2019; Bilal et al., 2017; Patel et al., 2018), inoculated with bio-inoculants according to the rate of applied N fertilizer. Meanwhile, studies on the variations in productivity and quality of dual-purpose triticale under variable integrated mineraland bio-fertilization management are scarce. In the current study, it was hypothesized that the application of Azotobacter chroococcum would reduce the need for mineral N fertilizer, and would uplift the productivity of dual-purpose triticale production system, in comparison to grain-only system under the Egyptian farming conditions. The objective of this study was to evaluate the performance of triticale grown in dual-purpose and grain-only production systems under variable rates of mineral N application, accompanied with Azotobacter chroococcum seed inoculation. Materials and methods